Acquisition of iron bound to strong organic complexes, with different Fe binding groups and photochemical reactivities, by plankton communities in Fe-limited …
Maria T. Maldonado, Robert F. Strzepek, Sylvia Sander, Phillip W. Boyd
Though it is clear that plankton in oceanic regions access iron bound to strong organic ligands, the mechanism... more Though it is clear that plankton in oceanic regions access iron bound to strong organic ligands, the mechanism mediating the release of iron from these complexes remains unresolved. In this study, we aim to elucidate the mechanisms of organic iron acquisition by plankton in subantarctic waters. In particular, we investigated the importance of photochemistry in mediating the reductive dissociation of iron from organic complexes, using naturally occurring ligands, and model iron complexes, with different iron-binding groups and photoreactivities. Our results demonstrate that iron within the model ligands is available for uptake and growth by indigenous plankton, but that photolability of these complexes does not determine iron bioavailability. In contrast, light significantly enhances iron acquisition from the in situ ligands, suggesting that the in situ iron ligands are photolabile, and that photochemistry in surface waters may play a significant role in iron uptake from the dissolved organic iron pool by oceanic plankton.
Download (.pdf) Spinning the ‘‘Ferrous Wheel’’: The importance of the microbial community in an iron budget during the FeCycle experiment
R. F. Strzepek, M. T. Maldonado, J. L. Higgins, J. Hall, K. Safi, S. W. Wilhelm, and P. W. Boyd
Several studies have shown the importance of the microbial community in specific aspects of the biogeochemical iron... more
Several studies have shown the importance of the microbial community in specific aspects of the biogeochemical iron (Fe) cycle such as uptake or regeneration. During FeCycle, a 10-day study of Fe biogeochemistry within an unperturbed mesoscale in situ SF6 labeled patch of HNLC waters, we investigated the role of both microzooplankton (herbivores and bacterivores) and viruses in regenerating Fe in the upper ocean. In summer 2003 we measured grazer-mediated Fe regeneration rates. The proportion of bacterial Fe released via grazing was severalfold greater than that mobilized from phytoplankton during herbivory. However, as the algal Fe pool (mainly Synechococcus) was severalfold larger than the bacterial pool, the absolute Fe regeneration rates were similar for both herbivores (17 pmol Fe L1 d1) and bacterivores (20 pmol Fe L1 d1). In all grazing experiments we observed that 90% (bacterivory) and 25% (herbivory)
of the labeled Fe resided in the dissolved fraction after 24 hours. This trend has previously been reported in similar laboratory culture studies, which invoked the formation of dissolved, and/or colloidal metal ligands, associated with digestion, to make the released Fe less bioavailable. This explanation may not be valid for our study as another FeCycle experiment (Maldonado et al., 2005) demonstrated that resident phytoplankton could obtain Fe bound to a wide range of strong-binding ligands. In situ estimates of virally mediated Fe regeneration during FeCycle ranged from 0.4 to 28 pmol L1 d1. It is not known why such a wide range of virally mediated regeneration rates was observed. Such variability prevented a direct comparison on the relative roles of grazers and viruses in Fe recycling. The rates of grazer-mediated regeneration accounted for 30% to >100% of the bacterial and phytoplankton Fe demand measured during FeCycle, indicating the key role of the microbial food web in Fe recycling.
FeCycle: Attempting an iron biogeochemical budget from a mesoscale SF6 tracer experiment in unperturbed low iron waters
P. W. Boyd et al.
An improved knowledge of iron biogeochemistry is needed to better understand key controls on the functioning of... more
An improved knowledge of iron biogeochemistry is needed to better understand key controls on the functioning of high-nitrate low-chlorophyll (HNLC) oceanic regions. Iron budgets for HNLC waters have been constructed using data from disparate sources ranging from laboratory algal cultures to ocean physics. In summer 2003 we conducted FeCycle, a 10-day mesoscale tracer release in HNLC waters SE of New Zealand, and measured concurrently all sources (with the exception of aerosol deposition) to, sinks of iron from, and rates of iron recycling within, the surface mixed layer. A pelagic iron budget (timescale of days) indicated that oceanic supply terms (lateral advection and vertical diffusion) were relatively small compared to the main sink (downward particulate export). Remote sensing and terrestrial monitoring reveal 13 dust or wildfire events in Australia, prior to and during FeCycle, one of which may have deposited iron at the study location. However, iron deposition rates cannot be derived from such observations, illustrating the difficulties in closing iron budgets without quantification of episodic atmospheric
supply. Despite the threefold uncertainties reported for rates of aerosol deposition (Duce et al., 1991), published atmospheric iron supply for the New Zealand region is 50-fold (i.e., 7- to 150-fold) greater than the oceanic iron supply measured in our budget, and thus was comparable (i.e., a third to threefold) to our estimates of downward export of particulate iron. During FeCycle, the fluxes due to short term (hours) biological iron uptake and regeneration were indicative of rapid recycling and were tenfold greater than for new iron (i.e. estimated atmospheric and measured oceanic supply), giving an ‘‘fe’’ ratio (uptake of new iron/uptake of new + regenerated iron) of 0.17 (i.e., a range of 0.06 to 0.51 due to uncertainties on aerosol iron supply), and an ‘‘Fe’’ ratio (biogenic Fe export/uptake of new + regenerated iron) of 0.09 (i.e., 0.03 to 0.24).
Inorganic carbon uptake by Southern Ocean phytoplankton
Philippe D. Tortell, Chris Payne, Celine Gueguen, Robert F. Strzepek, Philip W. Boyd, and Bjo ̈rn Rost
We report the results of laboratory and field studies examining inorganic carbon (Ci) utilization by Southern Ocean... more We report the results of laboratory and field studies examining inorganic carbon (Ci) utilization by Southern Ocean phytoplankton. Both in monospecific laboratory cultures of diatoms and Phaeocystis antarctica and in natural assemblages in the Ross Sea, Ci uptake by phytoplankton was dominated by direct HCO {3 transport. The contribution of HCO {3 transport to total Ci uptake ranged from 65% to 95%, with an overall average of ,80%. There was no significant difference among diatoms and Phaeocystis in the extent of HCO{3 transport. Extracellular carbonic anhydrase activity (eCA) was detected in eight of nine laboratory phytoplankton cultures and in all natural assemblages in the Ross Sea. The effective catalytic enhancement of HCO {3 : CO2 interconversion ranged from 1.5- to 13-fold (overall mean ,4-fold). Diatom-dominated Ross Sea assemblages had significantly greater eCA levels than did Phaeocystis-dominated assemblages. We found no strong correlations between Ci uptake parameters and in situ CO2 concentrations or chlorophyll a levels in the Ross Sea assemblages. Incubation experiments with natural assemblages showed that HCO {3 uptake and eCA expression did not change significantly over an 8-fold range in pCO2 (10.1–81.1 Pa), although total short-term C fixation rates increased under low CO2 conditions. Carbon-concentrating mechanisms are widespread among Southern Ocean phytoplankton and constitutively expressed by natural assemblages in the Ross Sea.
Adaptive strategies by Southern Ocean phytoplankton to lessen iron limitation: Uptake of organically complexed iron and reduced cellular iron requirements
Robert F. Strzepek, Maria T. Maldonado, Keith A. Hunter, Russell D. Frew, and Philip W. Boyd
We report results of laboratory studies examining the effect of low levels of iron (Fe) availability on the... more We report results of laboratory studies examining the effect of low levels of iron (Fe) availability on the intracellular Fe concentrations and specific growth rates in Southern Ocean diatoms (Fragilariopsis kerguelensis, Eucampia antarctica, Proboscia inermis, and Thalassiosira antarctica) and Phaeocystis antarctica. All species grew on Fe complexed to the siderophore desferrioxamine B (DFB). Concentrations of DFB up to 100-fold in excess of Fe were required to limit growth rates by ~ 50%. Southern Ocean phytoplankton also grew on Fe complexed by ~ 10-fold excess concentrations of the siderophores ferrichrome, enterobactin, or aerobactin, whereas the temperate coastal diatoms Thalassiosira weissflogii and Thalassiosira pseudonana did not. Intracellular Fe concentrations and Fe:C ratios of all Southern Ocean species were exceptionally low and decreased with decreasing Fe availability. However, large diatoms had significantly lower cell-volume–normalized Fe content and Fe : C ratios than Phaeocystis. Short-term Fe uptake and extracellular Fe(II) production measurements provided evidence that Phaeocystis possesses a reductive Fe transport pathway. Our findings demonstrate that the large- diatom Fe requirements are at least 2-fold lower than currently reported for oceanic algal species and suggest that bioreduction may enable resident phytoplankton to directly use Fe bound to strong organic ligands.
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Photosynthetic architecture differs in coastal and oceanic diatoms
Robert F. Strzepek & Paul J. Harrison
Diatoms are a key taxon of eukaryotic phytoplankton and a major contributor to global carbon fixation1. They are... more Diatoms are a key taxon of eukaryotic phytoplankton and a major contributor to global carbon fixation1. They are ubiquitous in the marine ecosystem despite marked gradients in environmental properties, such as dissolved iron concentrations, between coastal and oceanic waters. Previous studies have shown that offshore species of diatoms and other eukaryotic algae have evolved lower iron requirements to subsist in iron-poor oceanic waters, but the biochemical mechanisms responsible for their decreased iron demand are unknown2, 3. Here we show, using laboratory-cultured model species, a fundamental difference between a coastal and an oceanic diatom in their photosynthetic architecture. Specifically, the oceanic diatom had up to fivefold lower photosystem I and up to sevenfold lower cytochrome b 6 f complex concentrations than a coastal diatom. These changes to the photosynthetic apparatus markedly decrease the cellular iron requirements of the oceanic diatom but not its photosynthetic rates. However, oceanic diatoms might have also sacrificed their ability to acclimate to rapid fluctuations in light intensity—a characteristic of dynamic and turbid coastal waters. We suggest that diatoms, and probably other eukaryotic algal taxa, exploited this difference in the underwater light climate between oceanic and coastal waters, enabling them to decrease their iron requirements without compromising photosynthetic capacity. This adaptation probably facilitated the colonization of the open ocean by diatoms, and contributes to their persistence in this iron-impoverished environment.
Photosynthetic iron requirements of marine diatoms
PhD Thesis, University of British Columbia, 2003
Marine diatoms play a predominant role in the global carbon cycle but their growth is often limited by iron... more
Marine diatoms play a predominant role in the global carbon cycle but their growth is often limited by iron availability, especially in some oceanic regions. Diatoms from oceanic waters have lower iron requirements than coastal species, but the biochemical basis for this difference is unknown. The photosynthetic apparatus is a probable source of interspecific variability in iron requirements because it is both iron- rich and highly plastic, but it has not been examined in any oceanic diatom species.
I examined the phenotypic and genotypic variability in diatom iron requirements and measured for the first time the cellular concentrations of photosystems in a coastal and an oceanic diatom (Thalassiosira weissflogii and T. oceanica, respectively) acclimated to a range of irradiances and iron concentrations. Growth and photosynthetic rates, elemental composition, and photosynthetic pigments were measured. Photosynthetic electron transport chain complexes were quantified to construct a photosynthetic iron budget.
In iron-limited diatoms, nearly all the cellular iron was required for photosynthetic electron transport. Consequently, cellular and photosynthetic iron requirements co-varied with growth irradiance. Growth and photosynthetic measurements established that the increased iron requirement of low light acclimated cells did not appreciably heighten their susceptibility to iron limitation, or necessarily result in iron- light co-limitation, because the reduction in growth rate (Fe demand) at low light was greater than the increase in Fe requirements. The diatoms acquired comparatively more iron at low light by uncoupling rates of steady state iron uptake from growth and, in the
coastal diatom, by reducing cell volumes. Instead, diatoms were more iron-stressed growing near their maximum capacity under high irradiances.
The photosynthetic iron requirements of the oceanic diatom were substantially diminished: the cytochrome b6f complex and photosystem I, the most iron-rich complexes, were present at extraordinarily low concentrations compared to those found in coastal diatoms. The concentrations of these complexes were comparably low in Fe- replete cells, demonstrating that their abundance was not a consequence of iron deficiency. These results provide the first biochemical explanation for the low cellular iron requirements of an oceanic phytoplankton species.
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A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization
P. W. Boyd et al.
Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric... more Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the ‘iron hypothesis’. For this reason, it is important to understand the response of pelagic biota to increased iron supply. Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest. Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days. This drawdown was mostly due to the proliferation of diatom stocks. But downward export of biogenic carbon was not increased. Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters. Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction.
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The evolution and termination of an iron-induced mesoscale bloom in the northeast subarctic Pacific
P. W. Boyd, R. Strzepek, et al.
We initiated and mapped a diatom bloom in the northeast subarctic Pacific by concurrently adding dissolved iron and... more We initiated and mapped a diatom bloom in the northeast subarctic Pacific by concurrently adding dissolved iron and the tracer sulfur hexafluoride to a mesoscale patch of high-nitrate, low-chlorophyll waters. The bloom was dominated by pennate diatoms and was monitored for 25 d, which was sufficiently long to observe the evolution and termination of the bloom and most of the decline phase. Fast repetition–rate fluorometry indicated that the diatoms were iron-replete until day 12, followed by a 4–5-d transition to iron limitation. This transition period was characterized by relatively high rates of algal growth and nutrient uptake, which pointed to diatoms using intracel- lularly stored iron. By days 16–17, the bloom was probably limited simultaneously by both iron and silicic acid supply, because low silicic acid concentrations were evident. Modeling simulations, using data from our study, provided an estimate of the critical threshold for algal aggregation. Observed diatom abundances during the bloom exceeded this threshold between days 13 and 17. Mass sedimentation of diatoms and diatom aggregates was recorded in surface-tethered free-drifting sediment traps at 50 m in depth on day 21. Although the termination of the bloom was probably controlled by the availability of both iron and silicic acid, we cannot rule out the role of algal aggregation. The bloom decline was likely triggered by the onset of mass sedimentation. During our study, evidence of both diatom species succession and species-specific aggregation point to important links between algal nutrient stress and the initiation of algal aggregation.
Reconciling apparently contradictory observations
Gattuso J.-P. & Riebesell U., 2011. Reconciling apparently contradictory observations. In: Field C. B., Barros V., Stocker T. F., Qin D., Mach K. J., Plattner G.-K., Mastrandrea M. D., Tignor M. & Ebi K. L. (Eds.), Workshop report of the Intergovernmental Panel on Climate Change workshop on impacts of ocean acidification on marine biology and ecosystems, pp. 10-16. Stanford, California: IPCC Working Group II Technical Support Unit, Carnegie Institution.
Testing the effects of elevated pCO2 on coccolithophores (Prymnesiophyceae): comparison between haploid and diploid life stages
Fiorini S., Middelburg J. & Gattuso J.-P., 2011. Testing the effects of elevated pCO2 on coccolithophores (Prymnesiophyceae): comparison between haploid and diploid life stages. Journal of Phycology 47:1281-1291.
The response of Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler, Calcidiscus leptoporus (G. Murray et V. H.... more The response of Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler, Calcidiscus leptoporus (G. Murray et V. H. Blackman) J. Schiller, and Syracosphaera pulchra Lohmann to elevated partial pressure of carbon dioxide (pCO2) was investigated in batch cultures. We reported on the response of both haploid and diploid life stages of these three species. Growth rate, cell size, particulate inorganic carbon (PIC), and particulate organic carbon (POC) of both life stages were measured at two different pCO2 (400 and 760 parts per million [ppm]), and their organic and inorganic carbon production were calculated. The two life stages within the same species generally exhibited a similar response to elevated pCO2, the response of the haploid stage being often more pronounced than that of the diploid stage. The growth rate was consistently higher at elevated pCO2, but the response of other processes varied among species. Calcification rate of C. leptoporus and of S. pulchra did not change at elevated pCO2, whereas it increased in E. huxleyi. POC production and cell size of both life stages of S. pulchra and of the haploid stage of E. huxleyi markedly decreased at elevated pCO2. It remained unaltered in the diploid stage of E. huxleyi and C. leptoporus and increased in the haploid stage of the latter. The PIC:POC ratio increased in E. huxleyi and was constant in C. leptoporus and S. pulchra. Elevated pCO2 has a significant effect on these three coccolithophore species, the haploid stage being more sensitive. This effect must be taken into account when predicting the fate of coccolithophores in the future ocean.
Effects of elevated CO2 partial pressure and temperature on the coccolithophore Syracosphaera pulchra
Fiorini S., Middelburg J. J. & Gattuso J.-P., 2011. Effects of elevated CO2 partial pressure and temperature on the coccolithophore Syracosphaera pulchra. Aquatic Microbial Ecology 64:221-232.
The effects of elevated CO2 partial pressure (pCO2) and temperature on the coccolithophore Syracosphaera pulchra were... more The effects of elevated CO2 partial pressure (pCO2) and temperature on the coccolithophore Syracosphaera pulchra were investigated in isolation and in combination. Both the diploid and the haploid life stages were studied. Batch cultures were grown under four conditions: 400 μatm and 19°C; 400 μatm and 22°C; 740 μatm and 19°C; and 740 μatm and 22°C. The growth rate (μ) significantly increased at elevated pCO2 in the haploid stageonly and showed a different pattern with respect to temperature: it was higher at elevated temperature in the haploid stage at 400 μatm whereas it decreased in the diploid stage at 740 μatm. Increasing both parameters together increased the growth rate by 11% in the haploid stage only. Elevated pCO2 had a negative impact on the organic carbon (POC) content, production and cell size in both life stages at 19°C, while no significant effect was observed at 22°C. Increasing temperature significantly increased the POC content and production of the diploid stage at 740 μatm while at 400 μatm it significantly decreased both POC content and production of the haploid stage. Simultaneous increase of pCO2 and temperature had a negative effect on the POC content and production of the haploid stage only. Neither the calcification rate (PIC production) nor the inorganic:organic carbon ratio (PIC:POC) were significantly affected by elevated pCO2, temperature or their interaction. These results showed a strong interactive effect between pCO2 and temperature in affecting S. pulchra physiology, often more pronounced in the haploid life stage. Elevated pCO2 had a stronger effect than temperature. The rain ratio of S. pulchra will not be reduced by ocean warming and acidification.
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Impact of aragonite saturation state changes on migratory pteropods
Comeau S., Gattuso J.-P., Nisumaa A.-M. & Orr J., 2011. Impact of aragonite saturation state changes on migratory pteropods. Proceedings of the Royal Society of London. Series B: Biological Sciences
Thecosome pteropods play a key role in the food web of various marine ecosystems and they calcify, secreting the... more
Thecosome pteropods play a key role in the food web of various marine ecosystems and they calcify, secreting the unstable CaCO3 mineral aragonite to form their shell material. Here, we have estimated the effect of ocean acidification on pteropod calcification by exploiting empirical relationships between their gross calcification rates (CaCO3 precipitation) and aragonite saturation state Ωa, combined with model projections of future Ωa. These were corrected for modern model-data bias and taken over the depth range where pteropods are observed to migrate vertically. Results indicate large reductions in gross calcification at temperate and high latitudes. Over much of the Arctic, the pteropod Limacina helicina will become unable to precipitate CaCO3 by the end of the century under the IPCC SRES A2 scenario. These results emphasize concerns over the future of shelled pteropods, particularly L. helicina in high latitudes. Shell-less L. helicina are not known to have ever existed nor would we expect them to survive. Declines of pteropod populations could drive dramatic ecological changes in the various pelagic ecosystems in which they play a critical role.
Ocean currents help explain population genetic structure
by Rob Toonen
Management and conservation can be greatly informed by considering explicitly how environmental factors influence... more Management and conservation can be greatly informed by considering explicitly how environmental factors influence population genetic structure. Using simulated larval dispersal estimates based on ocean current observations, we demonstrate how explicit consideration of frequency of exchange of larvae among sites via ocean advection can fundamentally change the interpretation of empirical population genetic structuring as compared with conventional spatial genetic analyses. Both frequency of larval exchange and empirical genetic difference were uncorrelated with Euclidean distance between sites. When transformed into relative oceanographic distances and integrated into a genetic isolation-by-distance framework, however, the frequency of larval exchange explained nearly 50 per cent of the variance in empirical genetic differences among sites over scales of tens of kilometres. Explanatory power was strongest when we considered effects of multiple generations of larval dispersal via intermediary locations on the long-term probability of exchange between sites. Our results uncover meaningful spatial patterning to population genetic structuring that corresponds with ocean circulation. This study advances our ability to interpret population structure from complex genetic data characteristic of high gene flow species, validates recent advances in oceanographic approaches for assessing larval dispersal and represents a novel approach to characterize population connectivity at small spatial scales germane to conservation and fisheries management.
Spatial variability of recruitment in the sand crab Emerita analoga throughout California in relation to wind-driven currents
by Rob Toonen
We compared recruitment of the sand crab Emerita analoga over 2 yr at 17 sites distributed along >800 km of the... more
We compared recruitment of the sand crab Emerita analoga over 2 yr at 17 sites distributed along >800 km of the California coastline. We hypothesized that larvae of benthic invertebrates are retained by water circulation near headlands, and then redistributed alongshore north of the promontories during synoptic-scale relaxation in upwelling winds. We tested for a negative relationship between recruitment and distance north of 4 headlands: Point Arena, Point Reyes, Monterey Peninsula, and Point Conception. We also examined patterns of recruitment at sites east of Point
Conception, within the Southern California Bight (SCB). Recruitment magnitude was predictable at a given site within a recruitment season (June through October), but not between the 2 years at each site. Recruitment of E. analoga north of Point Conception was negatively correlated with site distance north of a headland in 1998, but not in 1999. Upwelling indices in 1998 were not significantly different from the long-term average either north of Point Conception or within the SCB; in contrast, during 1999, upwelling was stronger than the 54 yr average at all sites north of Point Conception, but not at those within the SCB. Thus, the upwelling-relaxation mechanism appeared to operate effectively from Point Arena to Point Conception in 1998, when upwelling and wind stress were within long-term average levels, but not in 1999, when upwelling and wind stress were anomalously high. However, in the SCB, we observed similar magnitude and spatial patterns of recruitment in both years. One implication of our results is that the California coast may be composed of separate retentive cells of populations separated by headlands, which enhances population persistence, but the extent
of larval loss from these cells remains unknown.
Weinbauer M. G., Mari X. & Gattuso J.-P., 2011. Effect of ocean acidification on the diversity and activity of heterotrophic marine microorganisms. In: Gattuso J.-P. & Hansson L. (Eds.), Ocean acidification, pp. 83-98. Oxford: Oxford University Press.
The effects of ocean acidification on microbial processes are very poorly understood despite the fact that marine... more The effects of ocean acidification on microbial processes are very poorly understood despite the fact that marine viruses and heterotrophic microorganisms play multiple roles in the functioning of marine ecosystems. Some information is available for the pelagic realm but the effects on benthic systems and on the interactions between microorganisms and marine animals remain unknown. Aggregates are hotspots of microbial activity and a main component of vertical fluxes. Since their formation is often stimulated at higher pCO2 levels, the net burial of carbon could be affected. Only neutral and positive effects were found on bacterial activity. Changes in the viral and microbial community composition were often observed in perturbation experiments. Since most effects of elevated pCO2 on microorganisms are poorly known and evidence is sometimes contradictory, the implications are highly speculative. Two non-exclusive scenarios are proposed, one resulting in a stimulation of carbon export to the deep-sea, the other in an increased remineralization of organic matter in the surface ocean and thus a reduced export. The net balance of these scenarios remains unknown.
Andersson A. J., Mackenzie F. T. & Gattuso J.-P., 2011. Effects of ocean acidification on benthic processes, organisms, and ecosystems. In: Gattuso J.-P. & Hansson L. (Eds.), Ocean acidification, pp. 122-153. Oxford: Oxford University Press.
The consequences of ocean acidification to benthic organisms and ecosystems could be significant but are, overall,... more
The consequences of ocean acidification to benthic organisms and ecosystems could be significant but are, overall, poorly known and quantified at this time. By integrating the current knowledge on the effects of ocean acidification on major benthic biogeochemical processes, individual benthic organisms, and observed characteristics of benthic environments as a function of seawater carbonate chemistry, it is possible to draw some general conclusions regarding the response of benthic organisms and ecosystems to a world of increasingly higher atmospheric CO2 levels. Large-scale geographical and spatial differences in seawater carbonate system chemistry, owing to both natural and anthropogenic processes, provide a powerful means to evaluate the effects of ocean acidification on marine benthic systems. Based on this approach, it is concluded that benthic biogeochemical processes such as calcification and CaCO3 dissolution as well as the community composition of benthic ecosystems will most likely be significantly altered by ocean acidification.
Rodolfo-Metalpa R., Houlbrèque F., Tambutté É., Boisson F., Baggini C., Patti F. P., Jeffree R., Fine M., Foggo A., Gattuso J.-P. & Hall-Spencer J. M., 2011. Coral and mollusc resistance to ocean acidification adversely affected by warming. Nature Climate change 1:308-312.
Increasing atmospheric carbon dioxide (CO2) concentrations are expected to decrease surface ocean pH by 0.3–0.5 units... more Increasing atmospheric carbon dioxide (CO2) concentrations are expected to decrease surface ocean pH by 0.3–0.5 units by 2100 (refs 1,2), lowering the carbonate ion concentration of surface waters. This rapid acidification is predicted to dra- matically decrease calcification in many marine organisms3,4. Reduced skeletal growth under increased CO2 levels has al- ready been shown for corals, molluscs and many other marine organisms4–9. The impact of acidification on the ability of individual species to calcify has remained elusive, however, as measuring net calcification fails to disentangle the relative contributions of gross calcification and dissolution rates on growth. Here, we show that corals and molluscs transplanted along gradients of carbonate saturation state at Mediterranean CO2 vents are able to calcify and grow at even faster than normal rates when exposed to the high CO2 levels projected for the next 300 years. Calcifiers remain at risk, however, owing to the dissolution of exposed shells and skeletons that occurs as pH levels fall. Our results show that tissues and external organic layers play a major role in protecting shells and skeletons from corrosive sea water, limiting dissolution and allowing organisms to calcify10,11. Our combined field and laboratory results demonstrate that the adverse effects of global warming are exacerbated when high temperatures coin- cide with acidification.
Effect of carbonate chemistry alteration on the early embryonic development of the Pacific oyster (Crassostrea gigas)
Gazeau F., Gattuso J.-P., Greaves M., Elderfield H., Peene J., Heip C. H. R. & Middelburg J., 2011. Effect of carbonate chemistry alteration on the early embryonic development of the Pacific oyster (Crassostrea gigas). PLoS ONE 6:e23010.
Ocean acidification, due to anthropogenic CO2 absorption by the ocean, may have profound impacts on marine biota.... more Ocean acidification, due to anthropogenic CO2 absorption by the ocean, may have profound impacts on marine biota. Calcareous organisms are expected to be particularly sensitive due to the decreasing availability of carbonate ions driven by decreasing pH levels. Recently, some studies focused on the early life stages of molluscs that are supposedly more sensitive to environmental disturbances than adult stages. Although these studies have shown decreased growth rates and increased proportions of abnormal development under low pH conditions, they did not allow discriminating between the direct physiological impact of pH decrease alone and the impact on calcification resulting from aragonite undersaturation, on the larval development of these species. In the present study, we aim at assessing the impact of various modifications in the carbonate chemistry by manipulating separately pH and total alkalinity on the growth of the Pacific oyster (Crassostrea gigas) larvae during the first 3 days of development (until shelled D-‐veliger larvae). Results showed that the developmental success (percentage of eggs developing to a viable D-‐veliger larvae) and growth rates were not directly affected by pH decreases but more likely by the associated decreases in aragonite saturation levels. In contrast to previous studies, both hatching and growth rates were not significantly altered as long as seawater remained saturated with respect to aragonite, and strongly decreased below saturation levels. These results suggest that the mechanisms potentially used by these organisms to regulate calcification rates are not efficient enough to cope for the low availability of carbonate ions under corrosive conditions.
Effects of ocean acidification on trace elements accumulation in the early life stages of squid Loligo vulgaris
Lacoue-Labarthe T., Réveillac E., Oberhänsli F., Teyssié J.-L., Jeffree R. & Gattuso J.-P., 2011. Effects of ocean acidification on trace elements accumulation in the early life stages of squid Loligo vulgaris. Aquatic Toxicology 105:166-176.
The anthropogenic release of carbon dioxide (CO2) in the atmosphere leads to an increase in the CO2 partial pressure... more The anthropogenic release of carbon dioxide (CO2) in the atmosphere leads to an increase in the CO2 partial pressure (pCO2) in the ocean, which may reach 950 ppmv at the end of the 21st century. The resulting hypercapnia (high pCO2) and decreasing pH (”ocean acidification”) may be expected to have appreciable effects on water-breathing organisms, especially on their early life stages. For organisms like squid that lay their eggs in coastal areas where the embryo and then paralarvae also exposed to metallic contamination, there is a need for information on how ocean acidification may influence their bioaccumulation. In this study, we investigated the effects of increased levels of pCO2 (380, 850 and 500 ppmv corresponding to pHT of 8.1, 7.85 and 7.60) on the accumulation of dissolved 110mAg, 109Cd, 57Co, 203Hg, 54Mn and 65Zn in the whole egg strand and in the different egg compartments during the whole period of development and in the hatchlings during their first days of the paralarval life. In the embryo, increasing seawater pCO2 enhanced the uptake of 110mAg and 65Zn and 203Hg showed a minimal concentration factor (CF) at 850 ppmv. The incorporation of 65Zn in statoliths increased with increasing pCO2 following its enhanced metal uptake in the whole body of the embryo and also with the greater size of the statoliths that occurred with their exposure to 850 and 1500 ppmv, compared to 380 ppmv. The more 110mAg, 203Hg and 65Zn accumulated in the embryo, the lower were their CF values in the eggshell, suggesting that the retention properties of the eggshell were affected by pCO2. The uptake of 109Cd and 54Mn in embryo and the eggshell decreased as a function of increasing pCO2 and the accumulation of 57Co in embryos was not affected by the pCO2 conditions. After 52 h of exposure, the steady-state equilibrium value of 110mAg CF in paralarvae increased with increasing pCO2, while the CF for 57Co was reduced at 1500 ppmv. As observed in the eggshell, 203Hg in paralarvae showed a maximal uptake rate at 850 ppmv whereas the uptake of 54Mn and 65Zn was not significantly modified by hypercapnic conditions. These results suggest a combined effect of pH on the adsorption and protective properties of the eggshell and of hypercapnia on the metabolism of embryo and paralarvae, both modifying the accumulation of particular metals in the biological tissues of Loligo vulgaris.